WO2010058276A2

WO2010058276A2 - Led source of light

Info

Publication number: WO2010058276A2
Application number: PCT/IB2009/007518
Authority: WO
Inventors: Giacomo Carcangiu; Roberto Faranda; Sonia Leva; Marcello Sardo
Original assignee: Politecnico Di Milano; Soltechna S.R.L.
Priority date: 2008-11-20
Filing date: 2009-11-19
Publication date: 2010-05-27
Also published as: WO2010058276A3; ITTO20080857A1

Abstract

A led source (1) of light has at least one led emitter assembly (2) adapted to emit a light beam and housed in an outer sealed casing (10), which houses a cooling liquid and is at least partially made of metal material to perform a function of heat exchanging with the outside.

Description

LED SOURCE OF LIGHT

TECHNICAL FIELD

The present invention relates to a led source of light.

BACKGROUND ART

The use of light sources comprising one or more leds, each of which comprises a supporting structure, an electroluminescent integrated device, hereinafter referred to as a "chip", having electric contacts protruding outwards from the supporting structure and protected by an epoxy resin mass, is known in the field of led lighting. The chip and the epoxy resin are housed in an outer light-permeable casing made of plastic material.

The known sources of the above-described type, although used, are always limited in power because the specific structure and the materials used do not allow to dissipate the heat generated by the operation of the integrated device beyond certain limits.

Overheating and consequent high operating heat excursions should be carefully avoided and inhibited, also because the expansion coefficient of epoxy resins is in general very different from that of the material used to provide the chip, and therefore in the presence of high heat excursions, e.g. for outdoor applications, stresses affecting the operation of the chip which may be thus damaged over time by the epoxy resin instead of being protected, may be generated between the various parts .

These types of sources are known as "low power" sources and are thus mainly used in signaling applications.

The problem of dissipating the produced heat is partially solved by the so-called "high power" led sources, in which the supporting structure is associated with a heat exchanger element, normally made of aluminium alloy, and in some cases, connected to a cooling system.

In high power light sources, chip protection is often improved by providing a second casing outside the aforesaid casing and filling the space between the two casings again with epoxy resin. Although such a constructional mode either stiffens or reinforces the light source, on the other hand it causes one or more deviations of the light beam emitted by the chip when crossing the interface surfaces between the casings and the epoxy resins.

Precisely for the presence of the heat exchanger element and of the possible cooling circuit of the heat element itself, the known sources further have large cross dimensions, which determine the final dimensions of the led sources of light. Attempts for reducing the dimensions by using techniques of miniaturizing the various components led to implementing light sources which, in view of particularly high costs, however generate all but negligible overheating problems and actually prevent either miniaturization or increase of the power which may be dissipated by the device.

Furthermore, having a single exchanger element and/or possible cooling circuit of the exchanger element itself may results in impediments of positioning the light source.

DISCLOSURE OF INVENTION

It is the object of the present invention to provide a led source of light, which allows to simply and cost-effectively solve the aforementioned problems.

According to the present invention, there is provided a led source of light comprising at least one led emitter assembly and an outer casing for housing said emitter assembly; the emitter assembly comprising a supporting structure and at least one electroluminescent integrated device adapted to emit the light beam, characterized in that said casing houses a transparent cooling fluid. In the above-defined light source, the cooling liquid is preferably a polydimethylsilicone liquid conveniently having a thermal conductivity in the range between 0.10 and 0.20 w| (mK) and a dissipation factor at 25° and 50 Hz in the range between 0.00009 and 0.00015. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanying drawings which illustrate a non- limitative embodiment thereof, in which: figure 1 diagrammaticalIy shows a side elevation view of a preferred embodiment of the led source according to the present invention;

Figure 2 is similar to figure 1 and shows a variant of a detail in figure 1; and figure 3 shows a side elevation view substantially in blocks of a further variant of the source of light according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION In figure 1, numeral 1 indicates a led source of light as a whole.

In the particular example described, source 1 comprises a led emitter assembly 2 mechanically connected to a block 8 made of thermally dissipative material, known per se, for dissipating part of the heat energy produced by the emitter assembly 2.

In turn, the emitter assembly 2 and the block 8 are connected to the supporting structure 3, which may consist in a dielectric material body. The emitter assembly 2 then comprises at least two different electrodes 7A and 7B connected to the emitter assembly 2 and protruding outwards from the supporting structure 3.

These electrodes have the purpose of electrically connecting the emitter assembly 2 to the outer power source of the device.

Again with reference to figure 1, the source of light 1 further comprises an outer sealed casing 10 for covering and protecting the emitter assembly 2. The outer casing 10 rests on the supporting structure 3 made of dielectric material surrounding the block 8 made of thermally dissipative material. The outer casing 10 consists of a cylindrical tubular body 13 in which an end portion is coupled to the fluid-tight supporting structure 3 and the opposite free end portion delimiting a closed axial opening 14, again fluid-tight, is coupled to a light-permeable body 15. The light-permeable body 15 conveniently consists of a common transparent or colored body. Alternatively, body 15 consists of an either mono or plurifocal, transparent or colored lens or set of lenses for either converging or scattering, and in general modifying, the light beam emitted by the emitter assembly 2, both geometrically and chromatically.

The tubular body 13 may also act as a heat exchanger if it is made of thermally dissipative material, conveniently an aluminium alloy. Otherwise, the increase of cooling capacity of the device is exclusively due to the increased heat exchanging surface between the emitter assembly 2 and the block 8, which is not now the contact surface between the emitter assembly 2 and the block 8 only, but also the contact surface between the block 8 and the cooling liquid.

Casing 13, along with the supporting structure 3, defines a sealed chamber 16, in which a cooling liquid is housed, having a crystalline appearance and thus excellent permeability to light. The cooling liquid is preferably a polydimethylsilicone liquid having a thermal conductivity in the range between 0.10 and 0.20 w| (mK) , a dissipation factor at 25° and 50 Hz in the range between 0.00009 and 0,00015, a fire point higher than 350° and a low heat power as compared to other class-K insulating liquids.

In the variant shown in figure 2, the outer casing 10 also houses a resin layer 18, conveniently but not necessarily of epoxy type, arranged to cover the emitter assembly 2, part of the supporting structure 3 and part of the block 8, so as to completely isolate the emitter assembly 2 from the polydimethylsilicone liquid. This variant may be advantageous if providing emitter assemblies 2 which are very robust to vibrations is desired, while improving the heat ^" exchanging properties of block 8 which is also cooled at the part being in contact with the refrigerating liquid in addition to the rear part thereof.

The embodiment shown in figure 3 relates to a source of light 20, which comprises a plurality of emitter assemblies 2 provided with a layer of epoxy resin or not, and arranged so as to be in contact with the base wall 21 of a sealed casing 22 at locations reciprocally side by side.

In addition to the base, the sealed casing 22 further comprises a common tubular body 23 made of the same material as the tubular body 13 and, as the tubular body 13, is frontally closed by a light-permeable body 24, made in the same manner as the body 15. The sealed casing 22 delimits a sealed chamber 25 either completely or at least partially filled with the same cooling liquid housed in casing 10.

It has been experimentally found that the use of a cooling fluid either instead of or along with traditional epoxy resins arranged about the emitter assembly 2 and inside the protective casing allows to increase the heat exchange with the outside, and thus the dissipation of heat generated by the emitter assembly 2, and inevitably to increase the power of the source of light. In addition to the cooling liquid effect, the heat exchange with the outside is greatly facilitated and amplified also by the constructional features of the outer casing (s) 10 and 22 which, unlike the casings of the known solutions may be made, in most cases, of highly dissipative materials, such as metal materials in general, and aluminium alloys in particular. By using outer casings with metal walls, the thermally dissipative surface is more than double as compared to the current constructional solutions and this allows to considerably raise the power of the current led sources of light, regardless they are of the high- or low-power type.

With regards to the light beam emitted by each of the emitter assemblies 2, instead, it is worth noting that the presence of the refrigerating liquid used does not at all obstruct the propagation of light waves, especially if the liquid belongs to the family of polydimethylsilicone liquids, which associate a perfectly crystalline appearance with a high thermal conductivity.

Again with regards to the propagation of light radiations, it is further worth noting that as compared to the known solutions, the propagation of light radiations in the described sources 1 and 20 is facilitated by the absence of refractive interfaces, if the outer casing 10,22 only contains the cooling liquid mass, while the distribution of the output light beam, its color and its color shade may immediately achieved either by varying the type of closing bodies of the tubular metal bodies 13 and 23 or introducing an appropriately colored liquid.

Finally, with regards to dimensions, it should be detected that the presence of the cooling liquid allows to increase the power of the source of light, the dimensions of the light source being equal, i.e. the dimensions of the outer casing being equal, but it especially allows to arrange many emitter assemblies 2 side by side because the cooling liquid in which they are immersed, along with the corresponding common containing casing, is able to easily dissipate the heat generated by the different emitter assemblies 2, even if these are arranged reciprocally side by side and in some cases even if they are free from the respective traditional heat exchangers.

From the above it is apparent that changes and variations may be made to the described sources of light 1 and 20 without therefore departing from the scope of protection defined by claim 1.

In particular, the described refrigerating liquid may be different from that disclosed by way of example, but again characterized by high refrigerating properties and marked by a crystalline appearance. The metal material used for making the outer casings 10 and 22 could also be different from that disclosed.

Claims

1. A . led source of light comprising at least one led emitter assembly adapted to emit a light beam; and an outer casing for housing said emitter assembly; characterized in that said casing houses a cooling liquid.

2. The source according to claim 1, characterized in that said cooling liquid is a polydimethylsilicone liquid.

3. The light source according to claim 1 or 2 , characterized in that said cooling liquid has a thermal conductivity in the range between 0.10 and 0.20 W| (mK) .

4. The light source according to one of claims 1 or 3, characterized in that said cooling liquid has a dissipation factor in the range between 0.00009 and 0.00015 at 25°C and 50 Hz.

5. The light source according to one of claims 1 to 3, characterized in that said cooling liquid has a fire point higher than 350⁰C.

6. The source according to any of the preceding claims, characterized in that said outer casing is made at least partially of a thermally dissipative material.

7. The source according to claim 6, characterized in that said outer casing comprises at least one dissipative portion made of an aluminium alloy.

8. The source according to any of the preceding claims, characterized in that it comprises at least one additional electroluminescent integrated device housed in said outer casing and at least partially immersed in said cooling fluid.

9. The source according to any of the preceding claims, characterized in that it comprises a mass of epoxy resin arranged in contact with said cooling liquid.

10. The source according to any of the preceding claims, characterized in that it comprises lens means arranged so as to close said outer casing to focus/uniform the light beam emitted by each electroluminescent integrated device housed in said outer casing.

11. The use of an electrically insulating and cooling liquid within a sealed casing of a led source of light comprising at least one emitter assembly adapted to emit a light beam.

12. The use of a polydimethylsilicone liquid within a sealed casing of a led source of light comprising at least one led emitter assembly adapted to emit a light beam.